Virgibacillus spp. stand out as a potent starter culture for accelerating the fermention of fish sauces and shrimp pastes. However, the underlying molecular mechanisms responsible for their adaptation and biotechnological potential remain elusive. Therefore, the present study focuses on phenotypic and genomic analyses of a halophilic bacterium Virgibacillus dokdonensis T4.6, derived from Vietnamese high-salt fermented shrimp paste. The draft genome contained 4,096,868 bp with 3780 predicted coding sequences. Genome mining revealed the presence of 143 genes involved in osmotic adaptation explaining its resistant phenotype to 24% (w/v) NaCl. Among them, 37 genes making up the complete ectoine metabolism pathway, confirmed its ability to produce 4.38 ± 0.29 wt% ectoine under 12.5% NaCl stress. A significant finding was the identification of 39 genes responsible for an entire degradation pathway of the toxic biogenic amine histamine, which was in agreement with its histamine degradation rate of 42.7 ± 2.1% in the HA medium containing 5 mM histamine within 10 days at 37 °C. Furthermore, 114 proteolytic and 19 lipolytic genes were detected which might contribute to its survival as well as the nutrient quality and flavor of shrimp paste. Of note, a putative gene vdo2592 was found as a possible novel lipase/esterase due to its unique Glycine-Aspartate-Serine-Leucine (GDSL) sequence motif. This is the first report to reveal the adaptative strategies and related biotechnological potential of Virgibacillus associated with femented foods. Our findings indicated that V. dokdonensis T4.6 is a promising starter culture for the production of fermented shrimp paste products.

The purpose of the study was to illustrate the roles of three primary indexes, namely sunlight, ventilation and stirring, in the \'bask in sunlight and dewed at night\' technique on the quality of shrimp paste, through a laboratory-scale design. The results showed that changes in the post-ripening fermentation conditions, especially sunlight, was instrumental in the physicochemical properties of the shrimp paste. E-nose and SPME-GC-MS were employed to assess the volatile flavor of post-ripening fermentation. A total of 29 key volatile aroma components played a crucial role in the development of post-ripening flavor in shrimp paste with or without sunlight. Lipidomic analysis revealed that sunlight promoted the oxidative degradation of FA, resulting in the production of a diverse range of flavor compounds that imparted the unique aroma of shrimp paste. The findings of this study will establish a theoretical basic for better control of the post-ripening fermentation of traditional shrimp paste.

The fermentation process of traditional shrimp paste is closely associated with the production of flavor substances, but the formation mechanism of key aroma components is still unclear. In this study, a comprehensively flavor profile analysis of traditional fermented shrimp paste was carried out by E-nose and SPME-GC-MS. A total of 17 key volatile aroma components with OAV > 1 contributed greatly to the overall flavor formation of shrimp paste. In addition, high-throughput sequencing (HTS) analysis revealed that Tetragenococcus was the dominant genera in the whole fermentation process. Moreover, metabolomics analysis showed that the oxidation and degradation of lipids, protein, organic acids and amino acids produced a large number of flavor substances and intermediates, which laid the foundation for the Maillard reaction in term of generating the distinct aroma of the traditional shrimp paste. This work will provide theoretical support for the realization of flavor regulation and quality control in traditional fermented foods.

A moderately halophilic, Gram-stain-positive, spore-forming rod-shaped bacterium, designated SKP2-8 was isolated from a traditional fermented shrimp paste (Ka-pi) collected from the market in Samut Sakhon province, Thailand. This isolate SKP2-8 was closely related to Allobacillus halotolerans LMG 24826T with 99.56% similarity based on 16S rRNA gene sequence. The draft genome of SKP2-8 was 2.53 Mb with 2,515 coding sequences with an average G+C content of 39.5 mol%. The ANIb, ANIm, AAI and the digital DNA-DNA hybridization values of isolate SKP2-8 were 97.22%, 97.64%, 97.75% and 78.0%, respectively, compared with A. halotolerans LMG 24826T. Based on the phenotypic characteristics, DNA-DNA relatedness and phylogenomic analysis, it was identified as Allobacillus halotolerans. The genome sequence data of this isolate provide information for further analysis of the potential biotechnological use of this microorganism and guide the characterization. The draft genome was deposited at DDBJ/ EMBL/GenBank (DNA Databank of Japan/European Molecular Biology Laboratory/Genbank) (VMHF00000000).

The present study focused on the determination of color, flavor, taste, and volatile organic compounds (VOCs) changes of shrimp paste fermented for 1, 2, 3, and 8 years by E-nose, E-tongue, and headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS). During fermentation, the color of shrimp paste turned dark brown with decreases in L*, a*, and b* values. Inorganic sulfide odor was dominant in all fermented samples. The umami, richness, and aftertaste-B reached a maximum in year 3 of fermentation. A total of 182 volatiles, including long-chain alkanes, esters, aldehydes, olefins, ketones, acids, furans, and pyrazines, were detected. Sixteen VOCs including dimethyl disulfide, methional, trimethyl-pyrazine, (E,E)-2,4-heptadienal, benzeneacetaldehyde were selected as flavor markers. Correlation analysis showed that 94 VOCs were related to saltiness while 40, 17, 21, 22, and 24 VOCs contributed to richness, umami, aftertase-B, sourness, and bitterness, respectively. These novel data may help in optimizing fermentation duration to achieve target flavor indicators in opossum shrimp paste production.

Retaining the traditional flavor while shortening the fermentation cycle is the current research focus for shrimp paste fermentation technology. The present study investigated the effect of combined use of halophilic bacteria as starters on the sensory and flavor characteristics of rapidly fermented shrimp paste. Sensory evaluation indicated that the starter-inoculated samples had high texture, appearance, and overall quality scores. Headspace gas chromatography-ion mobility spectrometry/mass spectrometry (HS-GC-IMS/MS) identified 95 volatile compounds, the fingerprint profiles of the starter-inoculated samples were similar to those of the traditional sample. Notably, the content of benzaldehyde, phenylethylaldehyde, and 3-methylbutyraldehyde increased significantly in the starter-inoculated samples (p < 0.05), which may provide an intense malt, caramel, and pleasant odor. Although the content of certain flavor substances in the starter-inoculated samples was lower than those of traditional sample, the use significantly reduced the fermentation time and mimicked the flavor profile of traditional shrimp paste to some extent.

The main purpose of the present study was to investigate the influence of two fermentation temperatures (10 °C and 20 °C) on the physicochemical properties and bacterial community composition of the low-salt shrimp paste. The physicochemical properties pH values, total volatile basic nitrogen (TVBN), amino acid nitrogen (AAN) and biogenic amines (BAs) of low-salt shrimp paste were analyzed and compared. The bacterial community composition was analyzed by high-throughput sequencing technology. Results indicate that the pH value fluctuated between 8.50 and 7.95, and the AAN, TVBN and total BAs levels of low-salt shrimp paste increased gradually after fermentation started, but the AAN content fluctuated steadily after 12 w. The contents of TVBN and total BAs in shrimp paste fermented at 10 °C were lower than those at 20 °C. Thus, the appropriate fermentation temperature and period were 10 °C and 12 w, respectively. Carnobacteriaceae and Staphylococaceae were the predominant family for the fermented shrimp paste. At the genus level, Alkalibacterium was predominantly present at 8 wk (96.36%), while Staphylococcus became the predominant one at 20 wk (58.71%). Correlation analysis shows that Alkalibacterium was positively associated with tyramine (R2 = 0.59), and Staphylococcus and Tetragenococcus were positively associated with AAN and TVBN. These findings are used to facilitate the quality control and improvement of low-salt shrimp paste production process in the future.

Two strains of moderately halophilic, Gram-stain-positive and spore-forming rods, designated as SKP4-8T and SKP8-2T isolated from shrimp paste (Ka-pi), were taxonomic studied based on polyphasic approach. Strain SKP4-8T grew at pH 6.0-9.0 (optimum 7.0), at 25-45 °C (optimum 37 °C) and in 1-16% (w/v) NaCl (optimum 5-10%). Strain SKP8-2T grew at pH 6.0-9.0 (optimum 8.0), at 25-45 °C (optimum 37 °C) and in 0-20% (w/v) NaCl (optimum 3-10%). The strains contained meso-diaminopimelic acid in cell-wall peptidoglycan and the major menaquinone was MK-7. Strain SKP4-8T contained iso-C15:0, anteiso-C15:0 and iso-C17:0; and strain SKP8-2T contained anteiso-C15:0, iso-C15:0, iso-C16:0 and antesio-C17:0 as major cellular fatty acids. Phosphatidylglycerol, diphosphatidylglycerol, unknown phospholipids and an unknown glycolipid were detected as major polar lipids. On the basis of 16S rRNA gene sequence analysis, strains SKP4-8T and SKP8-2T belonged to the genus Allobacillus and were closely related to Allobacillus halotolerans LMG 24826T with 98.8% and 99.3% similarity, respectively. The comparative genome analysis based on average nucleotide identity (ANI) and digital DNA-DNA hybridization revealed that both strains showed the values below 95 and 70%, from each other and from Allobacillus halotolerans LMG 24826T, respectively. Based on the data from this polyphasic study, strains SKP4-8T and SKP8-2T represent novel species of the genus Allobacillus and the name Allobacillus salarius sp. nov. was proposed for SKP4-8T (= KCTC 33905T = LMG 30016T = TISTR 2499T); and Allobacillus saliphilus sp. nov. for SKP8-2T (= KCTC 33906T = LMG 29682T = TISTR 2558T).

An aerobic, Gram-stain-positive, endospore-forming, rod-shaped and moderately halophilic strain SKP4-6T, was isolated from shrimp paste (Ka-pi) collected from Samut Sakhon Province, Thailand. Phylogenetic analysis revealed that strain SKP4-6T belonged to the genus Halobacillus and was most closely related to Halobacillus salinus JCM 11546T (98.6 %), Halobacillus locisalis KCTC 3788T (98.6 %) and Halobacillus yeomjeoni KCTC 3957T (98.6 %) based on 16S rRNA gene sequence similarity. The digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) values between strain SKP4-6T and its related species were 18.2-19.3 % and 69.84-84.51 %, respectively, which were lower than the threshold recommended for species delineation. The strain grew optimally at 30-40 °C, at pH 7.0 and with 10-15 % (w/v) NaCl. It contained l-Orn-d-Asp in the cell wall peptidoglycan. The DNA G+C content was 44.8 mol%. The major fatty acids were iso-C15 : 0, anteiso-C15 : 0 and anteiso-C17 : 0. The predominant isoprenoid quinone was MK-7. Phosphatidylglycerol and diphosphatidylglycerol were present as major polar lipids. Based on this polyphasic approach, digital DNA-DNA relatedness and ANI values, strain SKP4-6T represents a novel species of the genus Halobacillus, for which the name Halobacillus fulvus sp. nov. is proposed. The type strain is SKP4-6T (=JCM 32624T=TISTR 2595T).

Pink pigmented facultative methylotrophic (PPFM) bacteria are ecologically distributed microorganisms. They have been isolated in many types of ecosystems like soil, water, air, in association with plants and even as pathogens in humans. However, a yet unexplored area for PPFM bacteria research is in food. Hence, the objective of this study was to establish the presence of PPFM bacteria in Philippine fermented food, in particular shrimp paste, and characterise them phenotypically and genotypically. A total of 13 PPFM bacteria were obtained from Philippine shrimp paste. Sequencing of the 16S rRNA gene revealed that the PPFM bacterial isolates belong to the genus Methylobacterium. A total of 35 phenotypic characterisations were performed that included morphological, biochemical and physiological tests. Phylogenetic tree was constructed to establish the genetic relatedness of the isolates. Morphological test results showed that all 13 isolates were consistent with the established phenotypic characters of the genus such as pink colony colour, Gram negative and rod-shaped. Biochemically, the use of API® 20 NE tests showed heterogeneity of results and physiological tests exhibited that the isolates are primarily mesophilic and halotolerant, being able to grow at 2% salt. Phylogenetic analysis showed that the isolates are Methylobacterium populi, M. dankookense, M. lusitanum, M. radiotolerans and M. zatmanii. This study confirmed the presence and diversity of PPFM bacteria in Philippine shrimp paste. Further studies are needed to show the functional activity of Methylobacterium in Philippine shrimp paste production.